An aircraft is propelled by several turbojet engines each housed in a nacelle also housing an assembly of annex actuation devices related to its functioning and ensuring various functions when the turbojet engine is in operation or shut down. These annex actuation devices notably comprise an electro- or hydromechanical actuation system for a thrust reverser and an electro- or hydromechanical system to actuate the cowling intended to allow maintenance operations on the turbojet engine.
The role of the thrust reverser, on landing of an aircraft, is to improve the aircraft's braking capacity by redirecting forwardly at least part of the thrust generated by the turbojet engine. During this phase, the reverser is able to send all or part of the gas flows ejected by the turbojet engine towards the front of the nacelle, thereby generating a counter-thrust which is added to the braking of the aircraft wheels. For this purpose, a thrust reverser either side of the nacelle comprises a mobile cowl which can be moved between a deployed position which opens a passage in the nacelle intended for the deflected flow during a braking phase, and a retracted position which closes this passage during normal operation of the turbojet engine or when the aircraft is at a halt.
At the present time, these actuation systems are chiefly applied via hydraulic or pneumatic cylinders. These cylinders required a transport network for a fluid under pressure obtained either by tapping air on the turbojet engine or by bleeding from the aircraft's hydraulic circuit. Said systems are cumbersome however and require heavy maintenance since the slightest leak in the hydraulic or pneumatic network may have damaging consequences both on the reverser and on other parts of the nacelle. Also, the hydraulic or air cylinders always deliver the maximum power available, which leads to early wear of the equipment.
To overcome these drawbacks related to pneumatic and hydraulic systems, nacelle manufacturers and component suppliers have sought to find a replacement and to use electric actuation systems as much as possible, so as to lighten the nacelle and simplify its functioning notably regarding necessary maintenance cycles and the management of hydraulic or pneumatic fluids. Some nacelle cowling already exists intended for turbojet engine maintenance which is actuated by electric cylinders, and a thrust reverser actuated electrically is described in document EP 0 843 089.
Electric actuation systems provide optimal energy management in relation to the actual power needed for functioning of these systems, whilst taking up less space in the nacelle and not requiring any circulation circuit for fluid under pressure. They also allow integration of control and electronic drive systems such as described in French applications 04.07096 07.07098 and 07.01058 for example.
The electronic management of actuation of the thrust reverser system entails numerous constraints.
First, the thrust reverser function is governed by stringent certification requirements intended to ensure the safety of the system. This certification procedure is most costly.
Next, the control and monitoring functions are generally included in an electronic engine controller (FADEC or EEC) which follows its own certification procedure. Therefore the monitoring parameters and threshold values able to trigger certain actions are hardly accessible and configurable without the engine controller having to undergo a new certification cycle, which is highly costly when the changes made are limited to only a fraction of the operating functions managed by the aircraft computer.